As the Internet, mobile communications and the like have become widespread, carrier networks provided by telecommunication carriers are shifting from TDM networks such as SONET/SDH (Synchronous Optical NETwork/Synchronous Digital Hierarchy) or the like to packet networks that utilize the Ether (registered trademark) techniques and the IP techniques. Also, redundant network configurations have been implemented in practical use in order to enhance the reliability of networks. The standardization related to redundant configurations is described in, for example, ITU-T G.8031 (Ethernet Protection Switching).
In a redundant configuration, a plurality of logical paths (for example, a work path and a protection path) are configured for one communication flow. A communication flow is identified by for example a MAC address, a virtual LAN identifier, etc. Also, a work path and its protection path are configured in different routes. A data packet of a communication flow is transmitted through for example a work path. In such a case, when a failure has occurred in the work path, the data packet of the communication flow is transmitted through the corresponding protection path. In other words, path switching is performed from a work path to a protection path.
FIG. 1 illustrates an example of a method of switching from a work path to a protection path. Transmission equipment 1000(1000A, 1000B) includes a plurality of IF (interface) units as illustrated in FIG. 1. A work path and a protection path are configured between the transmission equipment 1000A and the transmission equipment 1000B. The transmission equipment 1000A transmits a data packet through the work path. For this transmission, in the transmission equipment 1000A, ingress-side IF unit #1 sets destination information in the data packet so that the data packet is guided to egress-side IF unit #6. By so doing, switch SW guides the data packet to egress-side IF unit #6 and egress-side IF unit #6 transmits the data packet to the transmission equipment 1000B through the work path. Accordingly, the transmission equipment 1000B receives the data packet through the work path.
Transmission equipment 1000 transmits monitoring packets for example periodically through respective logical paths (i.e., a work path and a protection path). In FIG. 1, transmission routes of a monitoring packet are depicted by dashed lines. The transmission equipment 1000 monitors a failure in logical paths based on monitoring packets transmitted from a correspondent transmission equipment. In the transmission equipment 1000A for example, egress-side IF unit #6 receives, through a work path, a monitoring packet transmitted from the transmission equipment 1000B. Then, the CPU of IF unit #6 guides that monitoring packet to a monitoring unit. Further, the monitoring unit transmits that monitoring packet to ingress-side IF unit #1. Further, the CPU of IF unit #1 determines the state of the work path based on that monitoring packet (or based on the fact that a monitoring packet does not arrive).
When, for example, the CPU of ingress-side IF unit #1 does not receive a monitoring packet via IF unit #6, the CPU determines that a failure has occurred in the work path. In such a case, ingress-side IF unit #1 sets destination information in a data packet so that a data packet is guided to egress-side IF unit #7. Then, switch SW guides that data packet to egress-side IF unit #7, and IF unit #7 transmits that data packet to the transmission equipment 1000B through a protection path. Accordingly, the transmission equipment 1000B receives the data packet through a protection path. In other words, path switching is performed from a work path to a protection path.
A method of path switching from a work path to a protection path is described in for example Japanese Laid-open Patent Publication No. 2010-239593 (Japanese Patent No. 4724763).
It is desirable that path switching from a work path to a protection path be performed in a short period of time in networks having a redundant configuration. In a SONET/SDH network for example, it is required that a switching process be executed within 50 milliseconds. Accordingly, it is desirable that a switching process be executed within 50 milliseconds also in a packet network.
However, in the transmission system illustrated in FIG. 1, the CPU of an ingress-side IF unit monitors a monitoring packet being guided from an egress-side IF unit to the ingress-side IF unit via the CPU of a monitoring unit so as to perform the path switching. In other words, the path switching is implemented by a software process. This causes a possibility that a long period of time is taken from the occurrence of a failure in a work path until the completion of the path switching.
Also, it is possible to provide a plurality of logical paths in one physical link by using a multiplexing technique. In such a case, when a failure has occurred in that physical link, path switching has to be performed for the plurality of logical paths. However, in the configuration illustrated in FIG. 1, path switching processes for a plurality of logical paths are sequentially performed by software. It is now assumed for example that the software processing time required for the path switching for one logical path is 100μ seconds and 2000 logical paths are provided for a physical link in which a failure has occurred. In such a case, switching of all the logical paths requires approximately 200 milliseconds.